1. Field of the Invention
The present invention relates generally to a communication terminal apparatus such as a facsimile apparatus, and more particularly to a communication terminal apparatus capable of determining a symbol rate and a bit rate desirable for use in accordance with conditions of a line connected between a transmission side apparatus and a reception side apparatus.
2. Description of the Related Art
There has been developed a communication terminal apparatus which conforms to a predetermined communication standard such as ITU-T Recommendation V.34 (hereinafter abbreviated as V.34) or the like, and which can provide a reception side apparatus with information relating to a combination of symbol rates available thereto from among a plurality of symbol rates stipulated in the predetermined communication standard. In this way, a communication is made at a symbol rate and a bit rate determined by the reception side apparatus based on the provided information relating to the combination of symbol rates and the characteristics of a line connected therebetween.
The V.34 standard allows communications between communication terminal apparatuses at a bit rate in a range of 2.4 to 33.6 kbps. For realizing this communication on speed, V.34 provides a communication sequence, called line probing, for revealing the characteristics of a line connected between a transmission side apparatus and a reception side apparatus upon starting communication. Using the result of this communication sequence, the transmission side and reception side apparatuses may select for their communication one of six available symbol rates from 2400 to 3429, which are predefined by V.34, as shown in FIG. 1.
As is apparent from FIG. 1, a higher upper limit can be obtained for the bit rate as a higher symbol rate is selected. However, better characteristics are required for a line connected between a transmission side apparatus and a reception side apparatus for communications being performed at a higher bit rate. As is also apparent from FIG. 1, an available upper limit of the bit rate is lower for the lower symbol rates. Communication performed at such a low bit rate can be made even under bad conditions which result from poor characteristics of the line connected between a transmission side apparatus and a reception side apparatus.
While V.34 defines a bit rate range for each of the six available symbol rates, these ranges overlap as shown in FIG. 1. Accordingly, bad conditions due to the characteristics of a line are more acceptable for a communication being performed at a lower symbol rate even with the same bit rate.
In overseas communications, it is generally known that communication quality is generally low since the line connected between the transmission side apparatus and the reception side apparatus is routed through a plurality of communication business entities. Such low line quality causes problems such as longer communication time and higher susceptibility to errors.
In V.34, the characteristics of a line are measured and the measurement result is relied on to determine a symbol rate within a range of symbol rates common to a combination of symbol rates available to the transmission side and a combination of symbol rates available to the reception side, as well as to determine a bit rate.
However, since it is the reception side that finally determines the symbol rate and the bit rate, and ITU-T does not dictate the determination criteria, a communication terminal apparatus such as a facsimile apparatus, which does not have the ability to correctly measure the line characteristics, may tend to set a higher symbol rate and a higher bit rate upon starting a communication. In such a case, errors may frequently occur during communications, causing an increase in communication time, although the communication speed is high. As a result, the transmission side will be burdened with an increased communication rate paid thereby.
Some facsimile apparatuses conforming to ITU-T Recommendation V.17 or earlier have an overseas communication mode in which an upper limit is set to the bit rate within a range of bit rates essentially available thereto to apparently reduce the available bit rate, thereby making overseas communications more stable.
However, with this overseas communication mode, the bit rate is always limited during overseas communications irrespective of communication destinations, so that a communication with a certain destination may become excessively stable. This means that while communication errors are reduced, a longer communication time is required due to a limited bit rate, thereby resulting in an increased communication rate.
The present invention provides a communication terminal apparatus adapted to notify a reception side apparatus, connected thereto in response to a call made by the communication terminal apparatus through a line to a specified destination telephone number entered to the communication terminal apparatus, of at least information on a combination of symbol rates available to the communication terminal apparatus within a plurality of symbol rates defined by a predetermined communication standard, to communicate with the reception side apparatus at a symbol rate and a bit rate determined by the reception side apparatus based on the notified information on the combination of symbol rates and the characteristics of the line connected thereto. The communication terminal apparatus includes a telephone number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of a combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of destination telephone numbers, and communication control means responsive to a specified destination telephone number entered to the communication terminal apparatus upon initiating a call to determine whether or not the specified destination telephone number is limited in symbol rate with reference to the telephone number/limited symbol rate correspondence table, wherein the communication control means is operative when determining that the specified destination telephone number is limited in symbol rate to notify the reception side apparatus of a corresponding combination of limited symbol rates as information on a combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus.
The present invention also provides a communication terminal apparatus adapted to notify a reception side apparatus, connected thereto in response to a call made by the communication terminal apparatus through a line to a specified destination telephone number entered to the communication terminal apparatus, of at least information on a combination of symbol rates available to the communication terminal apparatus within a plurality of symbol rates defined by a predetermined communication standard, to communicate with the reception side apparatus at a symbol rate and a bit rate determined by the reception side apparatus based on the notified information on the combination of symbol rates and the characteristics of the line connected thereto. The communication terminal apparatus includes an identification number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of a combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of identification numbers, and communication control means responsive to a specified destination telephone number entered to the communication terminal apparatus upon initiating a call to determine whether or not a number sequence at the beginning of the specified destination telephone number is coincident with an identification number which is limited in symbol rate with reference to the identification number/limited symbol rate correspondence table, wherein the communication control means is operative when determining that the identification number is limited in symbol rate to notify the reception side apparatus of a corresponding combination of limited symbol rates as information on the combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus.
Preferably, the communication terminal apparatus may further includes communication state detecting means for detecting a symbol rate and a bit rate determined by the reception side apparatus and used to actually make a communication between the communication terminal apparatus and the reception side apparatus which is connected through the communication control means to the communication terminal apparatus through a line in response to a call made by the communication terminal apparatus to a destination telephone number stored in the telephone number/limited symbol rate correspondence table, and symbol rate limitation alleviating means responsive to a symbol rate detected by the communication state detecting means after the communication has been normally completed without producing errors, wherein when the detected symbol rate is the highest one of symbol rates included in the combination of limited symbol rates stored in the telephone number/limited symbol rate correspondence table corresponding to the destination telephone number, and when a bit rate detected by the communication state detecting means is an upper limit bit rate which can be set at the highest symbol rate, the symbol rate limitation alleviating means additionally sets a symbol rate one rank higher than the highest symbol rate within the combination of symbol rates essentially available to the communication terminal apparatus as the combination of limited symbol rates stored in the telephone number/limited symbol rate correspondence table corresponding to the destination telephone number.
The present invention further provides a communication terminal apparatus adapted to notify a reception side apparatus, connected thereto in response to a call made by the communication terminal apparatus through a line to a specified destination telephone number entered to the communication terminal apparatus, of at least information on a combination of symbol rates available to the communication terminal apparatus within a plurality of symbol rates defined by a predetermined communication standard, to communicate with the reception side apparatus at a symbol rate and a bit rate determined by the reception side apparatus based on the notified information on the combination of symbol rates and the characteristics of the line connected thereto. The communication terminal apparatus includes an identification number registration table for storing previously registered identification numbers, a country number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of a combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of country numbers, and communication control means responsive to a specified destination telephone number entered to the communication terminal apparatus upon initiating a call to reference the identification number registration table and the country number/limited symbol rate correspondence table, wherein the communication control means is operative when a number sequence at the beginning of the specified destination telephone number has been registered as an identification number in the identification number registration table, and when a number sequence subsequent to the identification number in the destination telephone number represents a country number registered in the country number/limited symbol rate correspondence table to notify the reception side apparatus of a combination of limited symbol rates corresponding to the country number, as information on a combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus.
The present invention further provides a communication terminal apparatus adapted to notify a reception side apparatus, connected thereto in response to a call made by the communication terminal apparatus through a line to a specified destination telephone number entered to the communication terminal apparatus, of at least information on a combination Of symbol rates available to the communication terminal apparatus within a plurality of symbol rates defined by a predetermined communication standard, to communicate with the reception side apparatus at a symbol rate and a bit rate determined by the reception side apparatus based on the notified information on the combination of symbol rates and the characteristics of the line connected thereto. The communication terminal apparatus includes a telephone number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of a combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of destination telephone numbers, an identification number registration table for storing previously registered identification numbers, a country number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of the combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of country numbers, and communication control means responsive to a specified destination telephone number entered to the communication terminal apparatus upon initiating a call to reference the telephone number/limited symbol rate correspondence table, the identification number registration table and the country number/limited symbol rate correspondence table, wherein the communication control means is operative when the specified destination telephone number is registered in the telephone number/limited symbol rate correspondence table to notify the reception side apparatus of a combination of limited symbol rates corresponding to the destination telephone number as information on a combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus, and the communication control means is further operative when the specified destination telephone number is not registered in the telephone number/limited symbol rate correspondence table, and when a number sequence at the beginning of the specified destination telephone number has been registered as an identification number in the identification number registration table and when a number sequence subsequent to the identification number in the destination telephone number represents a country number registered in the country number/limited symbol rate correspondence table to notify the reception side apparatus of a combination of limited symbol rates corresponding to the country number, as information on a combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus.
The present invention further provides a communication terminal apparatus adapted to notify a reception side apparatus, connected thereto in response to a call made by the communication terminal apparatus through a line to a specified destination telephone number entered to the communication terminal apparatus, of at least information on a combination of symbol rates available to the communication terminal apparatus within a plurality of symbol rates defined by a predetermined communication standard, to communicate with the reception side apparatus at a symbol rate and a bit rate determined by the reception side apparatus based on the notified information on the combination of symbol rates and the characteristics of the line connected thereto. The communication terminal apparatus includes an identification number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of a combination of symbol rates essentially available to the communication terminal apparatus, wherein combination of limited symbol rates is stored corresponding to each of identification numbers, a country number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of the combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of country numbers, and communication control means responsive to a specified destination telephone number entered to the communication terminal apparatus upon initiating a call to reference the identification number/limited symbol rate correspondence table and the country number/limited symbol rate correspondence table, wherein when a number sequence at the beginning of the destination telephone number has been registered as an identification number in the identification number/limited symbol rate correspondence table, the communication control means is operative, when a number sequence subsequent to the identification number in the destination telephone number represents a country number registered in the country number/limited symbol rate correspondence table to notify the reception side apparatus of a combination of limited symbol rates corresponding to the country number, as information on a combination of symbol rates available to the communication terminal apparatus, to make a communication with the reception side apparatus, and when the number sequence subsequent to the identification number in the destination telephone number does not represent a country number registered in the country number/limited symbol rate correspondence table to notify the reception side apparatus of a combination of limited symbol rates corresponding to the identification number, as information on a combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus.
The present invention further provides a communication terminal apparatus adapted to notify a reception side apparatus, connected thereto in response to a call made by the communication terminal apparatus through a line to a specified destination telephone number entered to the communication terminal apparatus, of at least information on a combination of symbol rates available to the communication terminal apparatus within a plurality of symbol rates defined by a predetermined communication standard, to communicate with the reception side apparatus at a symbol rate and a bit rate determined by the reception side apparatus based on the notified information on the combination of symbol rates and the characteristics of the line connected thereto. The communication terminal apparatus includes an identification number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of a combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of identification numbers, a country number/limited symbol rate correspondence table for storing a combination of limited symbol rates which is set by selecting a portion or all of the combination of symbol rates essentially available to the communication terminal apparatus, wherein the combination of limited symbol rates is stored corresponding to each of country numbers, and communication control means responsive to a specified destination telephone number entered to the communication terminal apparatus upon initiating a call to reference the identification number/limited symbol rate correspondence table and the country number/limited symbol rate correspondence table, wherein the communication control means is operative when a number sequence at the beginning of the destination telephone number is not registered as an identification number in the identification number/limited symbol rate correspondence table, and when a number sequence subsequent to the identification in the destination telephone number represents a country number registered in the country number/limited to symbol rate correspondence table to notify the reception side apparatus of a combination of limited symbol rates corresponding to the country number, as information on a combination of symbol rates available to the communication terminal apparatus to make a communication with the reception side apparatus.